• ByRouging Solutions Editorial Team  ·  23 September 2026

Onsite or Offsite Passivation: How to Decide

The question is rarely about chemistry. It is about whether the kit can leave the plant, and what that costs you in time and upset when it does.

What Does Onsite Passivation Actually Mean?

Treating the steel where it already sits, with no trip to a workshop and no crate. A vessel stays on its legs and a loop stays in its hangers, and the chemistry travels to them instead. Nothing comes apart beyond what access needs.

Offsite is the other way round. Parts come off, travel to a workshop with tanks, get dipped and come back. For small parts that is often the cleaner option, whatever passivation chemical you settle on. A bath wets every surface evenly, and nobody is working at height.

The choice usually settles itself once you look at the item. A 5,000 litre reactor welded into a mezzanine is not going anywhere. A crate of clamps and gaskets has no reason to stay.

Most plants we work with end up running both. A shutdown at a Baddi or Vapi site will typically send the small fittings out to a workshop. The fixed vessels and the loop stay where they are. Splitting the job that way is normal, and it usually finishes sooner than forcing every item down one route.

When Does the Work Have to Come to You?

When moving the kit costs more than treating it where it is. That is the honest test, and it is usually clear enough. Installed pipework, big vessels, and anything whose removal breaks a validated joint all point the same way.

There is a second trigger that people often miss. Some surfaces cannot be dipped at all, whatever their size. A weld joint on a standing tank wall has no bath that fits it. Neither does the inside of a frame someone built in position.

The product range follows that same split, which tells you the split is real. The CitriSurf 3050 sheet names the other option directly. "For large items where continuous spraying is not available, on-site, or spot treatment applications, ready to use versions CitriSurf 77 and CitriSurf 2210 are available".

Which Products Suit Onsite Passivation?

The ready to use ones, because nobody wants to mix a bath on a walkway or a ladder. Both onsite products arrive at working strength. Their sheets give the normal working concentration as "Use as received". That removes the ratio error that catches out diluted work.

It also removes a mixing step on a walkway, which is worth more than it sounds. Nobody has to carry a measuring jug up a ladder. There is no part-used drum of dilute solution left at the end of the shift, and no second guess about what was in it.

The two do different jobs. CitriSurf 77 "is provided in trigger sprayer bottles for applications where it is desired to spray the product on a local area". Its sheet asks that surfaces be "sprayed, immersed or wiped" until completely wet. It singles out "crevices or in areas where any rust or corrosion may have occurred".

CitriSurf 2210 exists for the surfaces that will not hold a thin liquid. Its sheet says so plainly. The product is supplied "in a high viscosity form for easy application on weld joints, vertical surfaces". It is meant for items "that cannot be conveniently dipped in a bath". That is the one to reach for on a standing tank wall.

What Does Offsite Work Give You?

Control, mostly. A bath holds its heat, and heat is what the concentrate wants. The CitriSurf 3050 sheet prefers 120 to 160F, which is roughly 49 to 71C. Heating a tank in a workshop is far easier than heating a vessel in a plant room.

Dipping also solves coverage. The bath wets every surface at once, including the bores and blind corners a sprayer reaches only if the operator is careful. That evenness is the best argument for sending small items out.

The cost of it is disruption. Every removed part is a broken joint to remake, a gasket to replace and a connection to re-qualify. That work sits on your critical path.

Does the Standard Cover Installed Systems?

It does, and the wording is worth knowing. ASTM A380 covers "recommendations and precautions for cleaning, descaling, and passivating of stainless steel parts, assemblies, equipment, and installed systems" (ASTM A380/A380M-25). The clause names installed systems alongside loose parts. So treating a new line in place is squarely within the practice.

There is a limit on the other side of that scope. The same clause set says the practice "does not cover decontamination or cleaning of equipment or systems that have been in service". A system that has been running is outside it. Our guide to what ASTM A380 covers works through the whole scope.

That matters for how you write the job up. New work built on site sits inside A380. An in-service loop being cleaned belongs with derouging, and the interval for that is a separate question we cover in how often to derouge.

How Do You Choose Between Onsite and Offsite?

Answer four questions about the item, in this order. The test is ours, and no standard sets one. Can it come off without breaking a validated joint? Can it be dipped once it is off? Can you rinse it properly where it stands? Can you contain and drain what comes off it?

Two yes answers on removal and dipping point offsite. Two yes answers on rinsing and containment point onsite. Mixed answers usually mean a mixed job, with the small fittings going out and the installed run treated in place.

Scale tips the balance as well. One vessel is easy to treat in place. Forty spool pieces are quicker through a bath, because the bath does them all at once while a sprayer does them one by one.

Access cost is the figure nobody counts. If reaching a surface needs scaffolding, a permit and two people at height, the cheap chemistry has stopped being the cheap job. That is easy to miss when you price the work.

Timing matters too. Onsite work has to fit the shutdown window, and the window is set by production. Offsite work can start early, because the parts leave before the plant stops, and that often buys back a day.

Rinsing is the step people underrate. Both routes need a thorough rinse with clean water and immediate drying. On a mezzanine that means planning where several hundred litres will go before anyone opens a bottle.

Containment is the partner problem. You have to collect, neutralize and dispose of spent citric solution under the site's own rules. A clean room has nowhere for it to go by default. Sorting that out before the day of the job is what separates a smooth shutdown from a messy one.

What Goes Wrong With Each Route

Onsite work fails on access and containment. An operator who cannot reach the back of a vessel wall leaves a patch untreated, and the ferroxyl test finds it later. Spent solution with nowhere to drain becomes a mess in a clean area.

Offsite work fails on refitting and records. Parts come back clean, then get handled with bare hands, or refitted with a gasket nobody logged. The treatment was fine, and the surface is dirty again.

Both routes fail the same way on paperwork. The location of the work changes nothing about the file. Either way, the job needs the product, the strength, the time and the rinse logged against that kit. Our note on passivation records sets out the full list.

Rouging Solutions runs both routes, and we choose item by item. We treat installed loops and vessels in place with the ready to use products. Removable fittings go to a heated bath. We log the same four readings either way.

Where to Start

Walk the line with a list, and mark each item movable or fixed. That single pass answers most of the question before anyone quotes you. On a medium plant it takes about an hour, with a notebook and a torch.

For the fixed items, check rinse access and drainage next. Those decide whether onsite work is practical at all. For the movable ones, count the joints you would have to break and then remake.

Then decide item by item. A mixed job is normal, and it usually costs less than forcing everything down one route. Our passivation team will walk the line with you and mark it up.

Frequently Asked Questions